1. Field of the Invention
The present invention relates to a microwave oven, and in particular to a microwave oven which is capable of improving a cooking quality and cooking time by elevating heat efficiency of a heater.
2. Description of the Prior Art
A microwave oven cooks foodstuff by utilizing molecular motion of the foodstuff by using 2,450 MHz microwave.
FIG. 1 is a perspective view illustrating a microwave oven according to the conventional technology, and FIG. 2 is a sectional view illustrating a microwave oven according to the conventional technology.
As depicted in FIG. 1 and FIG. 2, the microwave oven comprises a main body including a cavity 10 where the foodstuff is cooked, an electric room 12 installed various electric units, and a door 14 installed on the front of the main body for opening/closing the cavity.
The electric room 12 includes a magnetron 16 generating high frequency, and a high voltage transmitter 18 and a high voltage capacitor 20 for applying a high voltage to the magnetron 16.
In addition, a radiating fan 22 for cooling the electric parts by sucking the outer air and an operating motor (not shown) for operating the radiating fans are installed at the rear side of the electric room 12.
And, a tray 25 to be mounted on the foodstuff is installed in the cavity 10, and a transparent window 26 for seeing through the cavity when the door 14 is closed is installed on the door 14.
A heater 28 for providing heat inside of the cavity 10 in a cooking state and a heater housing 30 for covering the heater 28 are installed between the rear wall of the cavity 10 and a casing 11.
A plurality of discharge holes 30a for discharging the heat of the heater 28 into the cavity 10 and a plurality of suction holes for suctioning the inner air of the cavity 10 which is used for cooking the foodstuff to the heater 28 are formed on the inner rear wall of the cavity 10.
And, a blast fan 32 for making the air flow so as to circulate through the discharge holes 30a and suction holes 30b of the cavity, and an operating motor for operating the blast fan 32 are installed on the heater housing 30.
The operation of the above described conventional microwave oven will now be described.
First, when the blast fan 32 is operated in the cooking state, the inner air of the cavity 10 flows to the heater housing 30 through the suction holes 30b by rotary force of the blast fan 32.
The air flowed to the heater housing 30 is heated through the heater by heat exchange with the heater 28, and is discharged into the cavity 10 through the plurality of discharge holes 30a. 
The high temperature air discharged into the cavity 10 heats the foodstuff, and flows to the heater housing 30 through the suction holes 30b, accordingly the foodstuff can be cooked by repeating above process.
However, the above described conventional microwave oven does not comprise a heat transmission means for transmitting efficiently heat energy generated from the heater 28, accordingly heat efficiencies of convection energy and radiant energy are lower, therefore the efficiency of the heater 28 is lower and cooking efficiency of the microwave oven is worse.
It is an object of the present invention to provide a heating device of a microwave oven which is capable of increasing heat efficiency of the heater and cooking quality and cooking speed by improving a heat transfer structure of the microwave oven so as to heighten heat transmission efficiency between the heater and air.
To achieve the object, a microwave oven including a cavity having a certain area for cooking of the present invention comprises a flow path formed between a main body and the cavity so as to be connected from a side of the cavity to the upper surface of the cavity, a heater installed on the side of the flow path corresponding to the outer upper surface of the cavity for emitting heat, a discharge hole installed on the upper surface of the cavity corresponding to the lower portion of the heater for discharging the heat of the heater into the cavity, an inlet installed on the lower portion of the side wall of the cavity for making the air inside of the cavity flow to the flow channel, and a circulating fan installed on a certain portion of the flow channel for circulating the air inside of the cavity flowed through the inlet to the heater.
In addition, in the microwave oven of the present invention, there are a plurality of discharge holes installed as concentric circles centering around the discharge hole on the center portion, and it is advisable to form the discharge hole adjacent utmost to the circulating fan so as to be the smallest among the plurality of discharge holes.
In addition, in the conventional microwave oven of the present invention, there are the plurality of discharge holes installed along the width direction of the flow path, and it is advisable to form the discharge hole formed on the center portion so as to be the smallest among the plurality of discharge holes.
In addition, in the conventional microwave oven of the present invention, when the high temperature air circulated by the circulating fan passes through the discharge holes, the maximum discharge speed is maintained as air velocity 9xcx9c13 m/s, passage dimension is maintained as 26xcx9c38 cm2, air volume circulated through the discharge holes is maintained as 1.4xcx9c2.0 m3/min when heat value is 3 kW, when the heat value is bigger/smaller than 3 kW, the air volume is changed in proportion to the heat value.
In addition, in the microwave oven of the present invention, it is advisable to from a reflecting plate on the external surface of the heater so as to cover the heater in order to provide whole radiant energy emitted from the heater to the cavity.
In addition, in the microwave oven of the present invention, it is advisable to form a plurality of circulation holes on a portion corresponding to the circulating fan in order to pass the circulating air inside of the cavity.
In addition, in the microwave oven of the present invention, it is advisable to form the heater so as to be zigzag-curved, and a heating plate for increasing heating dimension is installed on the heater.
In addition, in the microwave oven of the present invention, it is advisable to install the heater so as to be crossed on the square with the flow direction of the circulating air in order to increase the quantity of heat transmission between the heater and circulating air by always getting a maximum temperature difference between the heater and the circulating air.
In addition, in the microwave oven of the present invention, it is advisable to install the heater so as to be inclined at a certain degree to the flow direction of the circulating air in order to increase the quantity of heat transmission between the heater and circulating air by always getting a maximum temperature difference between the heater and circulating air.
In addition, in the microwave oven of the present invention, it is advisable to form the plurality of heating plates having through holes at the center portion so as to be penetrated and contacted by the heater.
In addition, in the microwave oven of the present invention, it is advisable to form a contact protrusion on the circumference of the through holes of the heating plates in order to increase the contact surface with the heater.